The invention relates to motion picture projectors and more specifically to the motion picture film platter assemblies that are used in the projection rooms.
Up until about twenty years ago, the projection rooms in movie theaters required two projectors to show a movie film. The first projector ran the first reel of the movie and the second projector ran the next reel of film and if it was an exceptionally long movie the first projector was used again. In the past each reel was good for 30 to 40 minutes of viewing time. Before the projectionist removed the first reel he would rewind it so it would be ready for its next use.
Improvements in the film industry have produced motion picture film platter assemblies having two or more vertically spaced circular platters. These platters are approximately 48 inches in diameter and they support a large reel of film that has been spliced together from several reels of film of a movie picture. This produces a reel that can run 4 to 5 hours. This eliminated the need for a projectionist to use two projectors and eliminated rewinding and setting up the next reel during the running of a movie film. Also the take-off of the film strip from the reel would be from its inner perimeter and it would be returned from the projector and wound onto the outer surface of a center ring on another of the circular platters after it has passed through the projector. This eliminated the need for a projectionist to rewind films after they were shown.
The problem with existing motion picture film platter assemblies is the structure on the film feed-out unit that is removably positioned in the center of the circular platter. These film feed-out units have a swing arm having a roller mounted adjacent its outer end around which the film strip passes prior to passing through a series of a 35 mm or 70 mm film idler rollers. The distance that the swing arm can pivot is controlled by the spacing of keeper rollers positioned on both sides of the swing arm. The film projector pulls the film through at a constant speed. Since the diameter of the film being fed out on the platter changes throughout its 4 or 5 hours showing, it is necessary, that the speed of the platter be coordinated with the projector's speed so it does not damage the film by having a build-up of film on the reel and rubbing of the film against itself. It is the job of the swing arm to take into account the change in diameter of the film being fed out. As the swing arm travels between maximum allowable rotation to the left and maximum rotation to the right, electrical signals are sent to the motor for the circular platter directing it to speed-up or slow-down the rotation of the circular platter.
The present day film feed-out units are not entirely satisfactory and occasional build-up of film results in portions of the film strip rubbing against itself and causing surface damage.
It is an object of the invention to provide a novel film feed-out unit that eliminates the structure of a pivoting film guidance arm.
It is also an object of the invention to provide a novel film feed out unit that eliminates costly film surface damage that results in the existing film feed-out units.
It is another object of the invention to provide a novel film feed-out unit that eliminates mechanical structure and replaces it with an improved film proximity sensor.
It is an additional object of the invention to provide a novel film feed-out unit that has fewer mechanical parts thereby reducing maintenance and down-time.